The Houthis have turned extortion into a structured business, offering shipowners a 'customer-relations' email address to negotiate payments for safe passage

Yemen’s Iran-backed Houthi movement has released the crew of a cargo ship more than a year after its fighters hijacked the vessel in the Red Sea, as part of its campaign of attacks in support of Hamas in its war against Israel.

Prisoner releases have been seen as a bid to jump-start talks to end Yemen's war, which began when Houthi rebels seized the capital, Sanaa, in 2014.